Table 2. Sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) of selected SARI and ILI sign and symptom combinations for laboratory-confirmed influenza infection, South Africa, February 2009–April 2012.
| Case Definition | Comparison group | Number tested | Sensitivity % (95% CI) | Specificity % (95% CI) | PPV % (95% CI) | NPV % (95% CI) |
|---|---|---|---|---|---|---|
| SARI case definitions* | ||||||
| Any child aged 2 days to < 3 months with (i) suspected sepsis OR physician diagnosed LRTI irrespective of signs and symptoms, AND (ii) onset within the past 7 days (in use from February 2009 to present) | Did not meet case definition | 812 | 89.6 (82.4, 94.1) | 10.8 (8.7, 13.3) | 13.1 (10.8, 15.8) | 87.4 (78.8, 92.8) |
| Any child aged 3–59 months with (i) LRTI, including bronchiolitis or pneumonia or bronchitis or pleural effusion, AND (ii) onset within the past 7 days (in use from February 2009 to present) | Did not meet case definition | 2,486 | 94.3 (91.4, 96.2) | 12.9 (11.5, 14.4) | 15.8 (14.4, 17.4) | 92.9 (89.3, 95.3) |
| ILI case definitions* | ||||||
| Patients of all age groups, with (i) acute respiratory tract infection of recent onset (within 72 hours), AND (ii) sudden onset of fever, AND (iii) two or more of headache, myalgia, cough, sore throat (in use from 2009 to February 2012) | Did not meet case definition | 4,914 | 88.7 (87.3, 90.0) | 22.2 (20.7, 23.8) | 45.9 (44.4, 47.4) | 72.5 (69.4, 75.4) |
| Patients of all age groups, with an acute respiratory illness with (i) measured fever of ≥38°C, AND (ii) cough, AND (iii) onset within the past 7 days (in use from March 2012 to present) | Did not meet case definition | 4,914 | 89.7 (88.3, 90.9) | 28.7 (27.0, 30.4) | 48.3 (46.8, 49.9) | 78.8 (76.2, 81.2) |
*Only respiratory specimens collected during influenza seasons (May to September) were included in this analysis.